• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 220 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS552882: Used as current source

user2007042
Prodigy 55 points
Part Number: TPS552882
Other Parts Discussed in Thread: TPS55288

I think of using one of the TPS552882 parts for a solar panel powered system.  The characteristics of the system is:

  1. Solar voltage panel 50W, maxpower at 17.2Volt and 2.91Amp
  2. The destination of the power is a battery of supercaps, 10F and 15Voltmax
  3. I expect input voltage to vary from a few volts to max 25Volt and the available input current from almost zero to 3.25Amp
  4. I expect the supercap battery voltage to vary from below 5Volt to max 15Volt (or possibly 18Volt if I add one more cell)
  5. I have a separate circuit for balancing the super caps such that the battery appears as one single capacitor

Because the input power will vary with weather conditions and the supercap battery does not have a constant voltage and also have a much larger capapacity value than the Cout value in the datasheet I would like to somehow use the converter as a current source rather than as a voltage source.

I have a separate controller and algorithm for adjusting the power drawn from the solar panel in such a way, that the solar panel will always be loaded close to the maximum power point.  This algorithm relies on the ability to control how much power the converter draws.

My questions comes down to these:

  1. Can TPS552882 be operated in a stable mode when loaded by 10F?
  2. Can the ILIM input be used to control the output current from TPS552882 by connecting a controlled current sink to the terminal instead of R6?
  3. Can the output current be regulated all the way down to zero (or close)?
  4. Can you suggest other ways to use TPS552882 as a controlled current source?

Kind Regards
Per Gaarde-Nissen
Senior R&D
Khepri

  • 0
    TI__Mastermind 34201 points

    Hi Khepri,

    1. No. When TPS552882 is loaded by 10F supercap, the 10F supercap behaves like a big load so TPS55288 will enter into hiccup mode and cannot startup correctly. 

    2. ILIM pin only control the inductor average current, not the output current.

    3. No.

    4. Will you consider using TPS55288 (I2C) version? TPS55288 has a register to set output current limit and output current could be regulated to very low level.

  • 0 in reply to Zack Liu
    Prodigy 55 points

    Hi Zack

    Thanks for your reply.

    A few comments:

    1. If I add a circuit to precharge the supercap to above 0.8V then the TPS552882 should enter current limit mode before entering hiccup mode, according to paragraf 7.3.16 on page 19.  Do you aggree or did I miss something here?
    2. Referring to the figur 7.2 at page 13 it looks to me that the current sense is located such as to sense the output current.
      In buck mode that will be equal to the inductor average current, but not so in boost mode when the inductor current will be higher than the output current.
    3. Why not if possible with the TPS55288?  It seems that the only difference is that on TPS55288 the internal value for I_limit is set by a register instead of by a load current to the ILIM pin as on TPS552882?
    4. Unfortunately I don't see TI offering an EVM for TPS55288.  Is that correct?

    Regards
    Per Gaarde-Nissen

  • 0 in reply to user2007042
    TI__Mastermind 34201 points

    Hi Gaarde-Nissen,

    1. Yes, to trigger hiccup mode, the output voltage is below 0.8 V and the average inductor current is above the setting value, the TPS552882 shuts down the switching for 76 ms (typical) and restarts the soft start repeatedly. If you could precharge the supercap to above 0.8V, TPS552882 should enter output current limit mode or inductor average current limit.

    2. The Red circle in figure 7.2 is used for inductor average current limit/peak current limit protection and for device current loop regulation. The output current limit is sensed with ISP, ISN pin and the output current sensing resistor.

    3. TPS55288 output current limit can be set through I2C CDC register. You mentioned that you want output current be regulated all the way down to zero (or close). TPS552882 output current limit threshold is fixed at 50mV.

    4. You can find the TPS55288 EVM on TPS55288 folder page on ti.com.

  • +1
    Prodigy 55 points

    Hi Zack

    Thanks for your reply.

    After all I think I will end up with another more home made solution.

    This is because I realise that to be able to regulate for maximum input power from the solar panel it is primarily the input values I want to regulate.  The output voltage is more or less fixed and the current does not matter (in short term) because of the super cap battery.

    I guess it can be made more simple when the converter does not have to care about the output.

    Kindly
    Per Gaarde-Nissen